The invention relates to polyester compositions, methods to synthesize the compositions and articles made from the compositions.
Many polymer-based articles are manufactured by injection-molding, blow-molding or other molding processes. These molding techniques require the polymer system to have adequate melt strength and viscosity. Generally, polyesters having relatively high molecular weight have poor flow properties. High molecular weight polyesters can be made suitable for injection molding by solid phase polymerization of polymers, but this operation raises the cost of the polyesters substantially. Polyesters having relatively low viscosities generally have flow properties that are better than polyesters having relatively higher viscosities. However, polyesters having relatively lower viscosities have been found to produce articles with poorer mechanical properties.
In order to obtain polyesters having commercially useful mechanical properties such as high modulus, different approaches have been tried. For instance, fillers have been used to reinforce polyesters. However, addition of fillers often leads to brittleness and failure of the polymer, which can lower the impact strength of the resin. Addition of fillers can also cause processing difficulties, due at least in part to lack of compatibility of the filler with the polymer matrix and such incompatibility can also result in molding and flow-related problems. Although the use of impact modifiers in such compositions can improve impact properties, the use of impact modifiers has not been found effective in producing polyester having a combination of both useful tensile modulus and impact properties.
Inorganic fillers, which are used to reinforce polymers, affect the impact properties of molding compositions. However, when an organic filler, particularly, polytetrafluoroethylene (PTFE) is used as a filler, impact properties are impaired such that impact properties are lower than that with other mineral or glass fillers. Polytetrafluoroethylene (PTFE) fibers have also been used as fillers in polymer compositions to obtain polyesters having improved tensile modulus-ductility properties balance with some success. Unfortunately, the fibers can aggregate in the matrix resin, making it very difficult to obtain a uniform composition. Such compositions are not known to produce polyesters having a combination of both useful tensile modulus and impact properties.
Polytetrafluoroethylene and other fluoropolymers, sometimes used as fillers, have also been used as additives in thermoplastic polymers in order to improve certain properties of the polymers. The use of relatively small amounts, e.g., from about 0.1 to about 1 percent by weight, of a fluoropolymer as an anti-drip additive in flame retardant grades of thermoplastic resin molding compositions is described, for example, in U.S. Pat. Nos. 4,810,739, 4,579,906, and 4,810,739. The use of sintered PTFE in highly filled thermoplastic compositions as low friction additives is disclosed in U.S. Pat. No. 5,879,791. A drawback to the use of fluoropolymer additives exists, however, in that such additives have poor dispersibility in many polymers. Such compositions are not known to produce polyesters having a combination of both useful tensile modulus and impact properties.
For the foregoing reasons, there is an unmet need to develop a polyester composition that can provide a balanced combination of tensile modulus and impact properties.
For the foregoing reasons, there is an unmet need to develop methods for making polyester compositions that can provide a balanced set of tensile modulus and impact properties.
For the foregoing reasons, there is an unmet need to develop articles derived from such polyester compositions that can provide a balanced set of tensile modulus and impact properties.
For the foregoing, industry to develop technologies that can provide molding compositions having useful mechanical properties with polyesters, e.g., low molecular weight polyesters.
For the foregoing reasons, there is a need in the industry to provide compositions based on low molecular weight polyesters with useful mechanical properties including desired balance of tensile modulus and ductility properties.